1. Field of the Invention
This invention relates to magnetic tape cartridges, and more particularly to magnetic tape cartridge housings having a rigid base member and a resilient cover.
2. Description of the Prior Art
Belt driven magnetic tape cartridges have been available for some time. The cartridge typically includes a housing and various internal components such as tape, rotatable tape spools, and rollers on pins, belt drive means and the like. The housing includes a base plate, usually metal sides; and a cover, usually rigid plastic material. The housing typically includes means for connecting the cover to the sides and base plate. Typically, glue or removable connection screws are used.
In 1971, Phillips made available three-part metal frame cassettes, e.g. model LGH6003 and LGH6005. The cassette includes a metal frame cast in a composite mold having a movable third mold section which can form cassette guiding surfaces which are true cylinders perpendicular to the support planes. The cassette includes two thin plastic covers which are mounted on the upper and lower sides of the metal frame. The metal frame constitutes the tape guide and the side walls of the cassette housing. For a more detailed explanation of such cassettes, see Milants, U.S. Pat. No. 4,166,593, col. 2, lines 46-65.
Typically, belt drive cartridge housings include a base plate made in one punching operation. The plate is then thermo-flattened and a plurality of holes are machined (counter-sunk) on the base plate. A cover with four walls made from rigid plastic material fits over the base. The cover is typically held in place by four screws sunk into plastic standoffs in the cover and screwed into the base. When assembled it has been found that many of these cartridges lose their flatness. Additionally, it has been found that when pins are pressed into the base plate, even when great care is used, there is a tendency for them to become non-perpendicular, causing unsatisfactory cartridge performance and detracting from cartridge longevity.
As demand for backing up data stored on non-removable rigid disks has increased, the demand for precise tape transport cartridges also increased. Formerly, 1/4" tape cartridge capacity of three Mega Bytes was acceptable. Now, expected storage capacity is upwards of 40 Mega Bytes with recording densities of 10,000 FRPI (flux reversals per inch). The number of tracks has risen from four to ten more. Tape speed also has increased from 30 inches per second (IPS) to 90 IPS. These demands place high requirements on precise tape transport.
Current tape transport of belt driven magnetic tape cartridges needs to be improved to meet the above demands. One problem in meeting the increasing demands is the base plate, the foundation of tape transport systems. Additionally, the current pressed-in pins do not fall within adequate perpendicularity tolerances, they also cause vertical tape guiding and uniform speed results to be unsatisfactory for increased performance.
Improvements in tape cassettes have been made. For example, Milants U.S. Pat. No. 4,166,593 discloses a housing for a magnetic tape cartridge and a method of molding the housing. The housing includes a molded plastic lower part and a molded plastic cover. The lower part (base plate) includes a tape guide unit extending between two true cylindrical tape guides. The tape guide is integral with cassette locating surfaces. Milants also discloses reinforcement ridges in the lower part for improving the rigidity of the cassette. Milants is an inexpensive cassette having low rigidity, and the cover is specifically recited as being rigid (col. 1, lines 50-54).
Anglin et al, U.S. Pat. No. 4,102,516 discloses a belt driven magnetic tape cartridge having an improved tape tensioning system of the type which may be used in connection with the instant invention, that patent is incorported herein by this reference. The corner rollers of the belt drive system include a bowed washer with a central portion having a hole receiving the pressed-in roller pin and bearing against an end of the roller, with a pair of arms bearing against the cartridge frame, whereby a small amount of drag may be imparted to the roller.
Singer et al, U.S. Pat. No. 4,032,987 discloses an injection molded cassette including a reflective portion which is placed in reflective alignment between a light emitting device and a light receiving device to provide automatic motor shut-off of the tape machine.